Coffee bean: let's find out what it contains and its chemistry before and after roasting!

Coffee bean: all the secrets.

The two species Arabica and Robusta have differences not only in taste, as we have already seen, but also in quantitative terms in the chemical composition of the raw coffee bean and the roasted bean, which are then extracted to become our drink. Arabica contains less caffeine , while Robusta contains less fatty substances . Given this, the composition of the coffee changes greatly during roasting (roasting) or in the process that transforms green coffee into roasted coffee ready to be ground and used to prepare the drink.

The roasting process of the bean

It starts with a gradual loss of moisture until the beans reach around 160°C. At this point some organic substances begin to be lost and carbon dioxide is formed. The grains swell and their density is reduced. This is the moment in which many volatile substances are formed which determine the aroma of the roasted coffee and the brown pigments, the melanoidins. Above 200°C the chemical reaction becomes exothermic. Above 240°C the grain begins to burn with the formation of soot, which makes the taste more bitter and burnt.

The composition of the coffee

The best known component of our bean friend is caffeine. Its chemical name is 1,3,7-trimethylxanthine . Caffeine belongs to the family of purine alkaloids such as theophylline (from tea) and theobromine (from cocoa). During roasting, part of the caffeine volatilizes. The content in roasted coffee does not change significantly, given the similar percentage loss of humidity and other substances. Caffeine is a bitter-tasting substance but its most important feature, the one that made it known, is its pharmacological activity . Isolated by the German chemist Ferdinand Runge in 1820, caffeine has pain-relieving properties in high doses (not those of a cup of coffee). The life of caffeine in our body is short and there is no danger of accumulation. It is in fact absorbed at the gastrointestinal level and after 15-45 minutes, it reaches its maximum concentration in the blood. Then it decreases gradually disappearing after a few hours.

Chemical studies on coffee have brought to light more than 900 different substances

Other classes of compounds contained in coffee are minerals (potassium, calcium, magnesium, phosphates, sulphates, etc.). Potassium is completely extracted while preparing coffee and is found in the cup. The lipids (commonly called fats) and the waxes (in the cortical part of the bean) are mostly retained during the preparation of the drink by the filter (whatever type of filter is used) of the coffee maker. Proteins and amino acids are lost during roasting. Carbohydrates (sugars, also known as polysaccharides), including soluble ones (sucrose), are lost during roasting forming the volatile compounds of the aroma. Insoluble carbohydrates (cellulose), on the other hand, undergo a transformation (depolymerization) going to volatilize and in part remain, as complex polymers, in the coffee grounds.